The HART Protocol

The highway addressable remote transducer protocol is also known as the HART protocol, according to Neil G Pansey. The HART protocol can communicate digitally over wires that also carry mill ampere analog signals from field devices. The digital component of the HART can transmit information about a field device status, health or communication status and configurable parameters to a host control system at the same time as basic information such as process value or valve position is transmitted, notes Neil G Pansey. A HART compatible device can provide component and manufacturer information as well, and the range and engineering units of the field device. HART, according to Neil G Pansey, is not specific to any given manufacturer and it provides interoperability between different equipment suppliers as long as these suppliers meet the HART standards. Each manufacturer that participates in the HART convention is assigned an identification number by HART.

HART was developed by the HART Communications Foundation, according to Neil G Pansey. The HART Foundation is now known as the Field Comm Group, which is located in Austin, Texas and is independent of various manufacturers. Today, millions of field instruments support the HART technology. Neil G Pansey notes that it is important that HART is bidirectional, therefore whatever host that a user employs, whether a handheld communicator or a distributed control system, will be able to communicate directionally with a HART compatible field device.

Valve positioners can be provided that support HART communication, notes Neil G Pansey, for linear or rotary style valves. Valve positioners compare a control signal to a valve actuator's position and move the actuator accordingly. By feeding back the valve position and status to a host control system by means of the HART protocol, the user is provided with additional information on the valve performance and can validate that the valve and the process are performing to specifications. Valve positioners that are electro-pneumatic in nature can be provided with HART capability, as well as electronic positioners using alternating current and direct current, notes Neil G Pansey. The health of the positioner itself can also be monitored and modeled using HART data provided by the HART compatible positioner.

HART allows valves and valve positioners to be tuned quicker, notes Neil G Pansey. Valve diagnostic parameters such as travel speed, total stroke, cycle count, stick slip and shut off count can be monitored by a HART reader. HART compatible devices can be employed by themselves or on as part of a network of HART compatible field devices in communication with a host system. HART devices can also be equipped with a wireless field adapter which enables transmission of HART parameters over the air to a wireless compatible control system. This newer technology allows transmission of valve data as mentioned above without the need to construct field cable and accessories. HART communication protocol digital valve controllers can be designed for non-incendive, intrinsically safe, flameproof and explosion proof applications. Safety Instrumented System valves can be provided with HART compatible positioners as they operate to control valve safety shutdown functions, notes Neil G Pansey.

At the HART host end, asserts Neil G Pansey, use of configuration and monitoring software allows HART compatible field devices to be configured remotely. Files can be provided for use with HART host software that enable communications between a HART field instrument and a HART host. Due to the ease of downloading software, users can maintain the latest HART capabilities when new tools and parameters are made available by device manufacturers, notes Neil G Pansey. Performance diagnostics capabilities enable data to be provided quickly to owners and operators. Multivariable instruments can also provide HART compatible data streams, enabling further analysis at the host system. The HART protocol has been used with level, flow, temperature, pressure and analytical field devices successfully in multiple deployments across the industry, notes Neil G Pansey. The presence of HART in industry applications is likely to continue to increase due to the trust users place in HART generated data.